This invention relates to the epoxidation of olefins such as propylene by reaction of the olefin with hydrogen and oxygen using a noble metal on titanium or vanadium silicalite catalyst, an essential feature of the invention being that reaction conditions are maintained so that both high rate and high selectivity is achieved.
Epoxides constitute an important class of chemical intermediates useful for the preparation of polyether polyols, glycols, glycol ethers, surfactants, functional fluids, fuel additives and the like. Many different methods for synthesizing epoxides from the corresponding olefins have been described in the literature. A Japanese patent application assigned to the Tosoh Corporation and published in 1992 (Kokai No. 4-352771) proposed making propylene oxide by reacting propylene, hydrogen and oxygen using a catalyst comprising a Group VIII metal and a crystalline titanosilicate. U.S. Pat. Nos. 6,281,369, 6,005,123 and 6,008,388 are also relevant. As with any chemical process, it would be desirable to attain further improvements in epoxidation methods of this type and it is to such improvements that this invention is directed.
There are several important process features which must be carefully regulated in order to achieve the benefits of the present invention. Chief among these is conducting the reaction so as to maintain high hydrogen conversion while at the same time maintaining very low concentrations of hydrogen in the reacting gases. At the same time, moderate oxygen conversion and high oxygen to hydrogen partial pressure ratios are maintained. The reaction is a continuous one and is carried out in a fully back mixed CSTR or in a packed bed plug flow reactor with a high recirculation ratio.